A fuel cell has been proposed as a clean, efficient, and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack for various applications. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media (DM), such as carbon fiber paper, which facilitates a delivery of reactants, such as hydrogen to the anode and oxygen to the cathode. An MEA and DM preassembled together with a subgasket for the separation of reactant fluids is known as a unitized electrode assembly (UEA).
In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
The electrolyte membrane is typically formed from a layer of ionomer. The electrodes of the fuel cell are generally formed from a finely-divided catalyst. The catalyst may be any electrocatalyst that catalytically supports at least one of an oxidation of hydrogen or methanol, and a reduction of oxygen for the fuel cell electrochemical reaction. The catalyst is typically a precious metal such as platinum or another platinum-group metal. The catalyst is generally disposed on a carbon support, such as carbon black particles, and is dispersed in an ionomer.
The electrolyte membrane, the electrodes, the DM, and a subgasket, for example, in the form of the UEA, are disposed between a pair of fuel cell plates. The pair of fuel cell plates constitutes an anode plate and a cathode plate. Each of the fuel cell plates may have a plurality of channels formed therein for distribution of the reactants and coolant to the fuel cell. The fuel cell plate is typically formed by a conventional process for shaping sheet metal such as stamping, machining, molding, or photo etching through a photolithographic mask, for example. In the case of a bipolar fuel cell plate, the fuel cell plate is typically formed from a pair of unipolar plates, which are then joined to form the bipolar fuel cell plate.
The dimensions of unipolar and bipolar fuel cell plates are known to vary after many of the processing steps associated with manufacture of the fuel cell plates. For example, the fuel cell plates change shape and size due to the stresses and heat history imposed on the fuel cell plates during processing. During a stamping procedure, the fuel plate experiences spring back when it is released from a forming tool. During laser trimming, laser welding, and part-marking procedures, the fuel cell plate shrinks or otherwise distorts due to the heat that is transferred to the fuel cell plate by the lasing.
There is a continuing need for a method of accurately measuring, monitoring, and compensating for physical changes that occur throughout the manufacturing process of a fuel cell plate. Desirably, the measurements can be broken down to a smallest increment of the manufacturing process in order to realize the effects of that particular process on the fuel cell plate and direct process changes to minimize the effects.